1. Field of the Invention
The present invention relates generally to loading apparatus and more particularly to a cassette tape loading apparatus suitable for use with a cassette tape recorder in which a tape is drawn from a tape cassette, wrapped around a rotary head drum and then recorded or reproduced by a rotary head.
2. Description of the Prior Art
A known so-called M-type loading mechanism is a cassette tape loading mechanism by which a tape is drawn from a tape cassette loaded to a cassette tape recorder and wrapped around its rotary head drum. According to this M-type loading mechanism, a pair of tape drawing pins are moved along both sides of the rotary head drum in substantially parallel relation to each other so as to draw the tape from the loaded cassette.
FIG. 1 schematically illustrates an example of such and M-type loading mechanism which is used in a cassette tape recorder or the like.
Referring to FIG. 1, there is provided a rotary head drum or rotary drum 1 around which a tape 2 is to be wrapped, a supply reel 3 for supplying the tape 2, a take-up reel 4 for rewinding the tape 2, reel motors 5 and 6 used to rotate the supply and take-up reels 3 and 4, respectively, a central processing unit (CPU) 7 used to control the reel motors 5 and 6 or the like, revolution speed detectors 8 and 9, each formed of, for example, a frequency generator (FG), to detect the revolution speeds of the reel motors 5 and 6, a loading motor 10, a loading drive mechanism 11, a loading position detector 12, movable tape guides 13 to 16 driven by the loading drive mechanism 11 and fixed tape guides 17 and 18. During the loading of the tape 2, the loading drive mechanism 11 is operated through the loading motor 10 by a control signal from the CPU 7 to thereby move the movable tape guides 13 to 16 in the directions shown by solid line arrows, whereby the tape 2 is loaded onto the head drum 1 so as to establish the tape running system shown by dashed lines. Meanwhile, during the unloading of the tape 2, the movable tape guides 13 to 16 are moved in the directions opposite to the above mentioned solid line arrow directions to unload the tape 2 from the head drum 1 and the tape 2 is rewound around the supply and take-up reels 3 and 4 respectively as shown by solid lines having a large thickness.
According to the above mentioned M-type loading mechanism, it is ideal that upon tape loading, an equal tape length of the tape 2 is drawn from both the supply and take-up reels 3 and 4 of the tape cassette and wrapped around the rotary head drum and that upon tape unloading, the tape 2 is equally rewound around both the supply and take-up reels 3 and 4 and the tape 2 is accommodated within the tape cassette. If the above ideal tape loading and tape unloading are made, then even though the tape loading and tape unloading are repeated many times, the tape 2 would always be wrapped around the rotary head drum 1 at the same tape position. If the tape 2 is wrapped around both the supply and take-up reels 3 and 4 with equal tape length, it is possible that both the reel motors 5 and 6 apply equal torgue to produce a tape tension with which the tape 2 is prevented from being slackened upon tape loading and a tape tension with which the tape 2 is rewound around predetermined reels upon tape unloading. However, in most cases, the supply and take-up reels 3 and 4 differ from each other in their tape wrapping amounts. Under this condition, if both the supply and take-up reels 3 and 4 are applied with the same torque to carry out the tape loading/unloading, the ratio between the reel inertia response torque and the torque of tape tension would be broken to thereby make the actual tape supplied amount/tape rewound amount between the supply and take-up reels 3 and 4 different. As a result, the position of the tape 2 is displaced and, at every loading/unloading, the tape 2 is wrapped around the rotary head drum 1 at different tape positions. Further, if the tape winding amount between the supply and take-up reels 3 and 4 differs considerably, the tape 2 would be moved uselessly a great deal, so that, for example, upon tape loading, the tape 2 should be supplied from both the supply and take-up reels 3 and 4 but the tape 2 would actually be rewound on one of the reels.
In a home VTR (video tape recorder) which employs a tape cassette of relatively small size, the absolute amount of the tape is so small that a tape winding diameter ratio, which is the ratio of diameters of tapes wound around the reels, is small. Besides, since tape loading/unloading speed is slow, the above mentioned defect is negligible. For this reason, any particular control operation is not intended yet in the home VTR.
Meanwhile, a professional VTR used in a broadcasting station or the like is so arranged as to use a tape with a very long length to improve the picture quality. Further, a tape cassette is required to have the tape with a long length by the demand for long-recording/playback. This makes the tape casstte large in size. In this large-sized tape cassette, the tape winding diameter ratio between the supply and take-up reels is naturally large, so that the balance of the tape supply/rewind amount between the tape supply reel and take-up reel is broken upon loading/unloading to cause the tape to be moved in one direction.
Further, an automatic tape cassette transporting machine is used in the broadcasting station to automate the transmission of broadcasting programs. This automatic tape cassette transporting machine comprises a cassette rack in which a number of tape cassettes are incorporated and a plurality of VTRs, in which a tape cassette selected from the cassette rack is transported by a cassette carrier, loaded onto a VTR and then reproduced. In this case, it is required that the reproduction be continuously carried out so as to prevent the reproduction from being interrupted.
In order to continuously reproduce a number of tape cassettes, the playback time of each of which is as short as that of commercial and spot news, by the VTRs, the number of which is limited, it is required that the tape cassette selected from the cassette rack be loaded to the VTR as quickly as possible, the tape be drawn from the tape cassette and the VTR be placed in the standby mode, while after the playback of the tape is ended, the tape is returned into the tape cassette, the tape cassette is ejected from the VTR and transported by the cassette carrier and returned to the cassette rack. For this reason, the loading/unloading of the tape of the tape cassette is preferably carried out at a speed as high as possible. However, if the high speed loading/unloading is carried out using the large-sized tape cassette in which the tape winding diameter ratio between both the reels is large and in which the tape tends to move uselessly, the tape position is displaced and the tape can not be protected from being damaged due to the abnormal tape movement.
The above mentioned defects can be overcome by applying appropriate torques to the reels in response to the tape winding amounts of both the reels. However, it is not possible to detect the tape winding amounts on the reels within the tape cassette just after the tape cassette is loaded on the VTR, so that the above mentioned method can not be realized. In order to detect the tape winding amounts on the reels, it is proposed to slightly move the tape before it is drawn from the tape cassette and to detect the tape winding amount by the known method. This previously proposed method takes a lot of time and so it is not suitable for the high speed tape loading/unloading.